Home > Uncategorized > Why is reliability important?

Why is reliability important?

Hello!  So, the blogs have changed slightly.  This is going to be my blog for weeks 4 and 5.  I’m going to be discussing why reliability is important when we’re doing research.

So first, what is reliability? And how can we measure it?
I’m pretty sure that if you’re reading this blog then you know all about reliability in a study, but I shall briefly explain anyway.

Firstly, reliability is very closely linked with validity, but it’s important not to get the 2 mixed up. Validity is whether your test measures what you want it to measure.  Reliability is a little different.

What is it?

Reliability is simply the consistency of a measure.  We could consider our result reliable if we get the same one repeatedly.  So, if we conducted an experiment to see if mood is affected by weather and found that it was, would we also find that same result when the test was conducted again? (this is an example of test-rest reliability…which I’ll come to in a second).

If so, the results could be considered reliable.

How can we measure it?

There are actually many ways to test reliability:

  • Test-retest reliability – which is when a test is administered at 2 different points in time to assess the consistency of a test across time.
  • Inter-rater reliability – this uses 2 or more experimenters to score the test. The scores are then compared to compare the consistency of the rater’s estimates.
  • Parallel-forms reliability – this uses 2 different tests, which were created using the same content.
  • Internal consistency reliability – this is when 2 questions (most often on a questionnaire) ask the same thing.  If the 2 answers match, that shows reliability.

I have gone into these in very brief detail, and there is more detail if anybody wants it here:



Now, is reliability important in Psychological testing?   Well, of course it is.  If an experimenter got different results every time they did the test, then how would they know which results were the true ones?  They couldn’t answer their research question.  If they found from one test that weather does affect mood, and on another they found that weather has no effect on mood – does weather affect mood?  There’s no way to know because those results aren’t reliable.

Now, if that were the case then that’s when they might look at the validity of the study and see if it was something other than the weather affecting people’s mood – were they actually measuring what they set out to measure? (Which is where reliability and validity are so closely linked, and where it might be easy to get the 2 confused).

So, I shall end by saying that if results aren’t reliable, there’s probably no point in putting any store in these results at all.

I’m going to be having a couple of weeks off from writing my blogs (please, don’t cry), so see you all after exam week, and if you’re a 2nd year Psychology student at Bangor (which I’m sure you are) good luck in your exams!!


Categories: Uncategorized
  1. November 24, 2011 at 10:10 pm

    A very informative blog, I liked the way that you clearly defined reliability and also added in the types of reliability that are sometimes forgotten when it comes to writing blogs. I agree that reliability is important when it comes to psychological research. However, you could have mentioned the use of qualitative data and whether that is ‘reliable’. In cases such as interviews which are subjective there will be researcher bias and those studies cannot necessarily be repeated again and again. This is due to participants not always giving the exact same response, or researchers interpreting recordings in different ways. But over all a really good blog 🙂


  2. November 25, 2011 at 6:18 pm

    Very easy to read and informative blog.
    Poor reliability degrades the precision of measurement and reduces researchers’ ability to keep track on the changes in measurements in studies, and this is why it is important to have reliable results. For example, when carrying out a study that might possibly lead to a theory, however this can be rejected or criticised due to the different inconsistent results that were shown under the same procedure. For Freud’ study, his “Little Hans” case study cannot be reliable if the study was repeated, there is no guarantee that same results could be done under the same condition.
    Thank you.

  3. psychrno
    November 25, 2011 at 9:59 pm

    I agreed that with you that reliability is different from validity. It is true that reliability factor is important in many research findings. Reliability show us the consistency and the repeatability of the results. Though, reliability often closely related to validity, reliability does not measure validity. It is important to know if a data is reliable, doesn’t mean the data could be valid, of course a data can never be valid if the data is not reliable in the first place.


    Overall, it is quite informative about reliability , cheers =)

  4. February 21, 2012 at 2:50 pm

    i totally agree and I think reliability is a key part of psychological research. If we did not test for a high reliability of a study, then we could not be able to replicate the findings; which would be that they would be unscientific and subsequently not available to be applied to a greater population. if your results can not be applied to the public, then there is not much point in carrying them out if they may only apply to a very certain situation

  5. March 14, 2012 at 6:26 pm

    I agree with your blog and find reliability to be a key ingredient in any research. Because let’s admit it, with out reliability you have no legs to stand on and your research is flawed. As you know, reliability in psychology firstly refers to the consistency and precision of a measure in an experiment. For example if a test is designed to measure a trait (such as agreeableness) in a personality test, then each time administered to a participant, the results should show a pattern and be approximately the same. That is, being reliable the test should show that the person has the same personality trait across all questions that coincide with that trait.
    I like the way that you included all the ways to test reliability, Test-retest reliability, Inter-rater reliability, Parallel-forms reliability and Internal consistency reliability. This was very informative.
    However i do believe that briefly describing the relationship between validity and reliability would have defiantly added to your blog. For instance saying this that an experiment is reliable doesn’t mean that it is valid. Because a reliable measure is measuring something consistently but that doesn’t mean you are measuring what you want to measure.
    To conclude, Found you blog very informative and interesting.

  6. joyce omoihin
    April 28, 2013 at 4:58 am

    reliability and validity are interdependent on one another. this point is very importance and every psychologist shuld knw this relationship.

    • April 28, 2013 at 1:06 pm

      First of all, where was it said that they weren’t independent from each other? I said that they were closely linked, but it was important not to get the two mixed up. Second, I tend not to take my advice from people who can’t spell ‘independent’, ‘important’ or ‘know’ (or for that matter, use a simple spell checker). Also, you might want to look into how capital letters are used in a sentence. Thank you.

      • tom
        May 20, 2014 at 5:41 pm

        She did not misspell ‘independent’, she wrote ‘interdependent’. These are two interchangeable terms.

  1. November 25, 2011 at 5:22 pm
  2. November 25, 2011 at 6:20 pm
  3. February 21, 2012 at 3:15 pm
  4. March 14, 2012 at 6:44 pm

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